The present invention relates to satellite communication transmitting power control systems, and in particular to a precipitation loss compensation power control system for a satellite communication system operating in the submillimeter or millimeter band which is susceptible to precipitation.
For satellite communication systems operating in the submillimeter band, the transmitting power of an earth station is controlled in such a manner that it compensates for the precipitation loss of uplink signals. One example of such power control systems is shown and described in Japanese Patent Publication 58-84544. In the system described in this Patent Publication, the master earth station transmits a pilot signal to a satellite which receives and retransmits it to the master earth station while at the same time transmitting to it a beacon signal. These earth-bound signals are received and compared with each other by the master earth station. From the result of comparison is derived a control signal which regulates in a closed loop the transmission power level of the master earth station so that the effective isotropically radiated power (EIRP) of the retransmitted pilot signal is maintained constant. Each of a plurality of slave earth stations provides estimation on the precipitation attenuation of the uplink signal in accordance with a level variation that occurs in the regulated pilot signal to control its own power level. While this system is economically attractive as it eliminates the need to provide a beacon receiver, for each slave earth station the EIRP of the retransmitted pilot signal drops when precipitation exceeds a prescribed limit beyond which the master earth station's transmission power is out of control. Each slave earth station interprets this situation as the occurrence between precipitation loss of its down link and increase its transmission power. As a result, the transponder of the satellite is overloaded and intermodulation is likely to occur.